1. Field of the Invention
This invention relates to surgical instrumentation for incising tissue in a human body and more particularly to an instrument and method for incising a pathway through tissue overlying an anatomic cavity or region of lesser density and for placing a cannula within the incised pathway to provide access to the interior of the body.
2. Description of Prior Art
Surgical techniques employing endoscopes and accessory instruments introduced into the interior of the body through cannulas have become increasingly important in a field known as "endoscopic" surgery. A surgeon performing an endoscopic surgery in the abdominal cavity first inserts a Verress needle through the abdominal wall and insufflates the cavity with (CO.sub.2) gas to separate the wall from the internal organs. Trocars and other cutting instruments have been provided for puncturing or cutting a pathway through tissue overlying the abdominal cavity for cannula placement.
A trocar is a shafted instrument with a sharp tip that is used to puncture a pathway through tissue. Commercially available trocars typically are configured with a three-faced pyramidal piercing tip from which the name trocar is derived: trois (three) and carre (sides or faces). Trocars suffer from the disadvantage of requiring powerful thrusting forces to puncture a path through tissue. The sharp tip and edges of the trocar can cause injury to an internal organ upon the slightest contact. Attempts to shield trocar tips within reciprocating sleeves after penetration into an anatomic cavity are undesirable because such sharp tips must pierce fully into the cavity before the shielding sleeve is triggered.
Other cutting instruments for abdominal access rely on screw threads to reduce the required thrusting forces, but such instruments offer no shielding for their sharp tips after penetration into the abdominal cavity. Such threaded instruments rely on precautionary insufflation as the only means to prevent lacerations of internal organs as their sharp tips penetrate the abdominal wall. There is therefore a need for new instruments and methods for safely incising a path through tissue and more particularly for incising a pathway through the abdominal wall with or without insufflation of the abdominal cavity and for placing a cannula within the incised pathway.